1. Field of the Invention
The invention relates to incandescent lamps having a planar filament array and a reflector adjacent the filament. More particularly, the invention concerns single-ended incandescent lamps having a planar filament array of adjacent coiled sections supported between two insulative bridges transverse to the lamp axis, and having a structure for supporting a reflector parallel to and spaced from the filament array.
2. Description of the Prior Art
Single-ended incandescent lamps having a planar filament array, such as tungsten halogen projector lamps, have a lamp envelope with a pinch seal at one end and a fused tip portion at the opposite end formed from tipping off an exhaust tube. The frame supporting the filament array generally has a pair of spaced rigid frame conductors extending from the pinch seal in the axial direction of the envelope and a pair of spaced insulative bridges extending transversely between the frame conductors. Filament retainers extend from the insulative bridges to support the individual coiled sections of the filament array. The filament retainers may, for example, have hook-shaped ends which engage looped portions joining the filament sections at each axial end of the filament array.
In one type of single-ended projector lamp, the insulative bridges are formed directly on the two frame conductors, which pass through and are embedded in each bridge near the opposite ends of the bridges. In a second type of lamp, the rigid conductors extend only through the bridge nearest the pinch seal. The second insulative bridge has, in addition to the filament retainers, a pair of wire supports fixed therein which extend towards the first bridge and have ends which are adapted for sliding on the rigid frame conductors. This construction permits tensioning of the filament array because the second bridge may be pulled away from the first bridge after the filament sections have been hooked on their respective retainers. After correctly tensioning the filament, the ends of the wire supports of the second bridge are welded to the frame conductors.
U.S. Pat. No. 3,555,338 discloses a quartz halogen lamp of the first type described above. The reflector is held parallel to the filament array by a pair of rods which are welded to one of the rigid frame conductors, extend therefrom transverse to the filament array, and are welded to an edge of the reflector. However, the welds securing the rods to the rigid conductor are difficult to make because of the close proximity of the weld points to the outer filament sections of the filament array. Additionally, specially shaped welding electrodes, in which one electrode has a right angle tip, are required to weld the transverse rods to the frame conductors.
In lamps of the second type described above, the filament is connected to the respective frame conductors by slipping-a short coiled section at each end of the filament array over the ends of the conductors and sliding them towards the first bridge. The looped portions joining adjacent coiled sections of the filament array are hooked on the filament retainers of the first bridge. The coiled end sections of the wire supports for the second bridge are then slipped over the rigid frame conductors and the filament retainers of the second bridge are hooked to respective looped portions of the filament array. The close proximity of the coiled end sections of the supports of the second bridge and the short coiled sections of the filament array on the frame conductors causes the additional problem that there is not sufficient space to weld the reflector support rods to the frame conductors while permitting proper positioning of the reflector.
U.S. Pat. 3,445,713 discloses a halogen incandescent lamp having a single quartz bridge and a reflector support wire embedded in the quartz bridge and welded to the top of the reflector. The single quartz bridge has filament retainers for holding the ends of the filament sections furthest from the pinch seal while the ends of the filament sections closest to the pinch seal are secured by filament retainers embedded directly in the pinch seal. However, embedding the reflector support wire in a quartz bridge is not suitable for frames of the second type, in which the bridge furthest from the pinch seal is slidable with respect to the other bridge to tension the filament array, because the variable position of the second bridge would vary the position of the reflector with respect to the filament array. Additionally, in smaller sized lamps, embedding the reflector support wire(s) in the quartz bridges is not practicable because they interfere with the placement of the filament retainers which are also anchored in the quartz bridge.